1. Field of Invention
The present invention relates to increasing quality of a projected image. In one embodiment, the invention is a method and device and/or apparatus to reduce the visibility of a “screen door” artifact present in the video image projected by various light engines based on pixilated displays. One way by which this is accomplished is through horizontal and vertical dithering of lens elements in the projection lens. Also disclosed is a method/device that increases the resolution of the projected image and may be used in combination with dithered lens elements.
2. Discussion of Background
The video image projected by a light engine based on a pixilated display contains an undesirable, visually observable artifact that is often called a “screen door”. The appearance of the screen door is illustrated in FIG. 1. The name derives from the fact that the artifact consists of a grid of dark vertical and horizontal lines that outline every pixel. The visibility of the screen door is greatest in light engines based on High Temperature Poly Silicon microdisplays, is less visible in those based on Digital Light Processing microdisplays and is even less visible in those based on Liquid Crystal on Silicon (LCoS) microdisplays.
One of the quantities that define the quality of a projected video image is resolution. In pixilated displays this is determined, in part, by the number of pixels in the array. To project the highest quality image, it is desirable that the display resolution equal that of the resolving power of human vision (e.g. average resolving power, highest average resolving power, etc.). In the case of a display with a large screen diagonal (such as is commonly the case in HDTV), the pixel count of the display needs to be quite high. In practice, there are two approaches to adding pixels to the image:
(1) Additional same size pixels are added to the microdisplay. In this case, the physical size of the array and the microdisplay will grow. Unfortunately, the larger the microdisplay, the more expensive the microdisplay.
or
(2) Additional smaller pixels are added to the microdisplay such that the array size is kept constant. This approach may not be technically possible. In any case, it is likely to make the microdisplay more difficult to manufacture and will almost certainly increase the visibility of the screen door artifact.